1. Field of the Invention
The present invention relates to electrical overvoltage protectors, sometimes referred to as electrical surge protectors or lightning arresters, used to protect telephone transmission lines against voltage surges, and more particularly, relates to a shorting cage inserted in the arrester housing that permits a fail-safe short to occur upon removal of the overvoltage protector cartridge.
2. Description of the Relevant Art
Surge arresters or protective devices known in the prior art generally include a housing that contains a pair of spaced apart electrodes and a means for maintaining a protector cartridge between the electrodes. The protector cartridge may contain a pair of spaced apart carbon or a gas tube that define an arc or a discharge gap therebetween in order to ground excessive line voltages so as to protect both the equipment on the line and the line itself. With repeated overvoltage conditions and discharges, the carbon gap loses its effectiveness and a gas tube may also fail with continued use. Typical of these arresters, which may include fusing links and internal shorting mechanisms so that when an overvoltage occurs the fusing link melts permitting a short to occur from the line electrode to ground, are U.S. Pat. Nos. 4,128,855 issued to Gilberts on Dec. 5, 1978; Re. 29,391 issued to Kawiecki on Sept. 6, 1977; 4,002,952 issued to Menninga on Jan. 11, 1977; and 3,703,665 to Yereance, et al on Nov. 21, 1972.
All of these devices operate similarly, however, each device has a common shortcoming. Upon removal of the protector device the line remains open, thereby, providing no protection for the line or equipment attached thereto. All of the disclosed devices require that the protector be in position and in operating condition in order to afford the proper protection.
It is well known that when a serviceman dispatched to repair a shorted protector device, upon occasion, not having a replacement device available will return the protector cartridge without inserting the protector device therein. This condition may cause considerable damage should an overvoltage occur on the line because there is no indication that the protective mechanism is missing. The terminal or line when checked from the telephone line central office will read "open" and will indicate that the line is in good working order.
Therefore, it is an object of the present invention to provide a simple, inexpensive means for protecting telephone or other communication lines from overvoltage surges when the protector mechanism is removed therefrom.
It is yet another object of the present invention to provide a short from line-to-ground when the protective device is removed from its receptacle in a terminal block.
It is a further object of the present invention to provide a means for the central office to determine that the protective cartridge and/or protector device has been removed from a terminal protector block until a new cartridge and protector device has been replaced therein.
It is yet another object of the present invention to prevent a serviceman from replacing a defective protector cartridge without inserting a replacement protector device therein.